| Cold spray technology has great application potential in material repair,which can realize the remanufacturing of failed parts without the need to replace the parts as a whole.Aluminum alloy repaired or manufactured by cold spraying usually has high hardness and strength but poor plasticity,and its mechanical properties can be improved by heat treatment.The aluminum alloy repaired or manufactured by cold spraying also faces the problems of corrosion and wear protection.Plasma electrolytic oxidation(PEO)technology can generate oxide ceramic coating on the surface of the valve metals,which is a surface coating technology commonly used for aluminum alloy protection.In this study,cold spray technology was used to prepare 7075 aluminum alloy on a rolled 7075 aluminum alloy substrate.The microstructure and mechanical properties of cold sprayed 7075 aluminum alloy before and after heat treatment were tested and analyzed,and the T6 heat treatment process parameters were optimized.A PEO coating was prepared on the surface of cold sprayed and rolled 7075 aluminum alloy using plasma electrolytic oxidation technology,and the microstructure,mechanical properties,corrosion resistance and wear resistance of the coating were tested and analyzed.The sealing method is adopted to further improve the corrosion resistance and wear resistance of the coating.The results of the study are as follows:The particles in the cold sprayed 7075 aluminum alloy have undergone severe plastic deformation and have a fine-grained structure.Cold sprayed 7075 aluminum alloy has a dense structure,low porosity(0.7%),high strength(365MPa),high hardness(144HV0.03)and bonding strength(75.6MPa),but poor plasticity.After T6 heat treatment,the fine grain structure in cold sprayed 7075 aluminum alloy disappeared,the grain size became larger,the work hardening was eliminated,and the comprehensive mechanical properties were improved.The hardness and tensile strength were slightly reduced(142HV0.03 and 356MPa)),plasticity was increased(the strain at break by 150%)and the bonding strength was increased by 69%(127.8MPa).The PEO coating of cold sprayed 7075 aluminum alloy was mainly composed of?-Al2O3and little amount of?-Al2O3,with a thickness of about 15-20?m,and a small amount of internal defects such as micropores and microcracks.The hardness of the PEO coating reached 1353±156HV0.01,and the bonding strength exceeded 38MPa.After PEO treatment,the corrosion resistance of cold sprayed 7075 aluminum alloy was greatly improved.The self-corrosion current density dropped from 1.16×10-4A/cm2 by 3 orders of magnitude to 6.27×10-7A/cm2,and the corrosion potential also rose by about 0.1V.The wear resistance was also greatly improved,and the wear rate dropped by two orders of magnitude from 3.65×10-4mm3/N·m to 2.41×10-6mm3/N·m.After the sealing treatment,the self-corrosion current density of the PEO coating further dropped by an order of magnitude,reaching 1.45×10-8A/cm2;the sealing treatment can also improve the long-term corrosion resistance of the PEO coating,soaking in Na Cl solution for 1 or 7 days before the electrochemical experiments were performed.Compared with the unsealed samples,the self-corrosion current density of the sealed samples was two orders of magnitude lower,and the surface coating did not crack after the experiment.Sealing treatment can also reduce the friction coefficient at the initial stage of the wear tests and increased the critical load that the PEO coating can withstand.The sealing treatment further reduced the wear rate of the PEO coating samples,and the reduction decreased with the increase of the load(2N:13%;5N:7.1%). |
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